1. Field of the Invention
The present invention relates to a pipe coupling on which a plug can easily be connected or disconnected and particularly, a pipe coupling equipped with a ball valve as the valve member.
2. Description of the Related Art
Pipe couplings equipped with ball valves as the valve members are disclosed in Japanese Patent Publication Sho 51-47899 and U.S. Pat. No. 3,423,063. Such a pipe coupling has a fluid passage provided in the center of a ball valve thereof which is pivotably mounted in a valve chamber. The pipe coupling has at one end a pipe joint portion thereof to which a pipe is joined for supply of pressurized fluid such as gas or liquid. Also, a plug extending to a destination to which the fluid is supplied is detachably joined to the other end of the pipe coupling. While the pipe coupling is disconnected from the plug, its ball valve remains rotated to the closed position to shut down the fluid passage on the pipe side with a non-open spherical side (surface) of the ball valve.
When the pipe coupling is connected with the plug and its outer sleeve of a tubular shape is axially slid towards the plug, the sliding movement gradually drives the ball valve to pivotally rotate to the opened position. As the result, the pipe joint portion of the coupling is communicated via the fluid passage in the ball valve to the fluid passage of the plug.
For disconnecting the plug from the pipe coupling according to Japanese Patent Publication SHO 51-47899, the outer sleeve is moved towards the pipe joint portion in the reverse direction to the sliding movement for the connection. The reverse sliding movement causes the ball valve to gradually rotate back to the closed position. As the outer sleeve has been moved to a predetermined position, the ball valve completely shuts down the fluid communication between the pipe joint portion and the fluid passage in the plug. At the same time a mechanical engagement between the pipe coupling and the plug released.
For disconnecting the plug from the pipe coupling, an outer sleeve is first slid backward according to U.S. Pat. No. 3,423,063. The ball valve is set in an opened position, an inlet end is sealed and at the same time an outlet end is purged. Next, an inner sleeve is slid backwardly. A locking ball which engaged the plug with the outlet end is set free and the plug can thereby be released from the outlet end.
The conventional pipe coupling, however, has the following disadvantages.
(1) When the communication between the pipe joint portion of the coupling and the fluid passage in the plug has been shut down by the ball valve, the passage in the plug stays under pressure for a while. It is preferable, therefore, when the plug is to be mechanically disengaged from the pipe coupling, to purge a fluid in the plug to lower the inner pressure after the fluid passage is shut down.
In Japanese Patent Publication SHO 51-47899, the shut down of the fluid passage and the disconnection of the plug are executed in a succession by a single operation. It is thus difficult to carry out only the closing movement of the ball valve without the plug disconnection from the pipe coupling. When the operation for the disconnection is carried out, the plug is mechanically disconnected from the pipe coupling regardless of the magnitude of its inner pressure. If the outer sleeve is accidentally handled for removal before the inner pressure drops down to a given level, it is undesirably disconnected.
In U.S. Pat. No. 3,423,063, after the outer sleeve is slid for release and the pressurized fluid in the plug is purged enough, the inner sleeve should be slid for release. However, if the outer sleeve and the inner sleeve are operated quickly or the purge quantity is small relative to internal pressure, the plug can be disadvantageously released from the outlet before the internal pressure is decreased.
(2) The sealings between the opposite openings of the fluid passage in the ball valve and the fluid passages in the pipe and the plug are respectively realized with the sealing members such as packings. In the communicating mode, it is essential that the sealing members are highly stressed against regions about the openings of the fluid passage for optimum sealing effects. On the contrary, for rotating back the ball valve, it is necessary to allow the free movement of the ball valve without the stress. Such two opposite conditions can hardly be satisfied at one time.
(3) The ball valve is pivotably mounted but not supported by a pivot in the valve chamber. When the ball valve is rotated, therefore, it may divert from its essential rotating direction or perform a parallel movement, hence failing to move to the correct positions in the closing and opening operations.
(4) For communication of its fluid passage in the coupling, the ball valve is pivotally driven by the elastic force of a spring. In operation, the ball valve is actually driven by the elastic force during a portion of the period from the closed position to the opened position and then rotated by an internal force to the opened position. For avoiding any imperfect rotating movement to the opening position, the elastic force applied to the ball valve is relatively large. As the ball valve remains high in rotating speed even just before reaching the opened position, it will hardly be stopped at the opened position without error.
(5) When the sliding movement of the outer sleeve towards the plug for opening the valve is not adequate and the outer sleeve fails to reach the desired position, the ball valve is hardly rotated to the opened position.